Definitely an elm, probably a large-growing one (most are). Fruits are generally needed to positively identify wild species, in addition to those are many intentional hybrids, both old and new - and not fully represented in keys and descriptions. You can't count on someone coming up with a 100% reliable species identification based on seeing this picture on the internet. If it happens to be a comparatively distinctive kind that somebody suggests as a possibility then there you are, otherwise even unusually thorough and dedicated tree expert Arthur Lee Jacobson of Seattle, WA (author of NORTH AMERICAN LANDSCAPE TREES, TREES OF SEATTLE, PURPLELEAF PLUMS) cannot give airtight names to every elm tree he has encountered. And this is includes his home territory, probably the last stronghold (alas, no longer) of elms susceptible to Dutch Elm Disease and pretty much no longer represented by full-sized specimens elsewhere.

Hello, Joopster. I noticed no mulch under on the soil under the tree so please make sure to add some organic mulch, up to 3-4" to the drip line. Your idea to use sticks is a good one as these tree-form hydrangeas tend to collapse under windy conditions. Once the root system is big enough, the need for them will disappear but in the meantime, protect them with those bamboo sticks or metal stakes, basically whatever you can find that will keep them from collapsing when the wind blows. If the area is not windy, the bamboo sticks may be enough. If it is windy, consider something more sturdy. These guys have a big chunk of the weight on the top. Add wind/storms and those moving stems/flowers.etc will cause problems if not staked. Same thing happens to standard roses. Feel free to water whenever the soil feels almost dry or dry to a depth of 4". Once the plant goes dormant, you can further reduce waterings to once a week or once every two weeks. And of course, stop watering when the ground freezes. Don't bother fertilizing now, not just because it is so late in the growing season for you, but because the potting mix probably already contains those round fertilizer pellets. Fertilize in Spring instead and enjoy the blooms you now have! Use a 1/2 to 1 cup of compost, composted manure or cottonseed meal only once in the Spring. Then use weak fertilizers like coffee grounds, iquid seaweed and liquid fish thru the end of June to prevent the plant from staying active instead of going dormant. By the way, the blooms can be deadheaded (not pruned) or left for winter interest. I leave them on the plants and they always manage to disappear by magic sometime after January/February/March. Luis

You could splint it with bamboo (see link in bottom of post) but I'm not sure if that would be needed. I would simply driveve two 8 foot stakes into the ground (would need to soak the ground for a bit in your climate) and tie as shown in the picture. One to pull it straight and the other to stabilize it. Search for "sturdy stake 8ft" and you will see what stakes that shold be sturdy if driven at angle away from the tree. Home depot, Menards, etc.. all have them. To pull it straight you will want a good a good material that will not dig into the bark. I have had great luck with Arbor Tie and you can buy on Amazon or you could use something similar and much less expensive, but you can reuse it over and over if you don't mind getting a large amount at once. Either way, check out this YouTube video on how to tie a knot without hurting the tree... https://youtu.be/KUCceRETFL0 It will move with the wind but as it grows and gains caliper it should stay start to hold this position. https://books.google.com/books?id=gXg-oWDB8dgC&pg=PA154&lpg=PA154&dq=gillman+mew+leader+spliny&source=bl&ots=s7pK3XMxCC&sig=SfiQTccdaPwzYhjQLrTAYuy5uUA&hl=en&sa=X&ved=0ahUKEwjpxKSurv7NAhVH2oMKHVYKAZsQ6AEIHTAA Good luck, and before you know it this thing will be taking off!

smartdesigner- I generally have a negative reaction when people want to classify bamboo as a nuisance based on their fear it will get out of control and devour the neighborhood. However, your situation is exceptional. If you are not allowed to use the normal, effective bamboo controls, then I think that approaching the city with the position that this could become a nuisance situation is a good strategy and kind of puts the ball in their court. They would have to either say that you aren't allowed to control it and worry about the consequences if it moves out and compromises the area, or they can decide that a modest barrier is going to do more good than harm. Or they could decide to get your neighbor to remove it. He might still get annoyed, but you wouldn't be the sole target. Installing barrier means trenching down maybe 24 inches, which means groundwater would still be able to move, and if the barrier was kept an inch or two above ground level, surface water could move over it when the area gets a lot of water. I understand that they don't want to have people building diversionary dams, but I would argue to them that bamboo barrier doesn't constitute that level of habitat alteration. (Between you and me -- and something you don't need to share with the city -- is that, although bamboo do like water, they do not like too much water. Bamboo will typically not move through a stream bed, and they begin to suffer and die when their root systems are continuously subject to standing water for several weeks. So it's hard to know in your situation what bamboo will do in this environment.) However, approaching the city with your concerns is wise as this shouldn't have to fall all on you. Good luck and post back when you have more to share.